Cell-cycle-specific cDNAs from mammalian cells temperature sensitive for growth

S100a6 knockdown promotes the differentiation of dental epithelial cells toward the epidermal lineage instead of the odontogenic lineage

Tooth development is a complex process involving various signaling pathways and genes. Recent findings suggest that ion channels and transporters, including the S100 family of calcium-binding proteins, may be involved in tooth formation. However, our knowledge in this regard is limited. Therefore, this study aimed to investigate the expression of S100 family members and their functions during tooth formation. Tooth germs were extracted from the embryonic and post-natal mice and the expression of S100a6 was examined. Additionally, the effects of S100a6 knockdown and calcium treatment on S100a6 expression and the proliferation of SF2 cells were examined. Microarrays and single-cell RNA-sequencing indicated that S100a6 was highly expressed in ameloblasts. Immunostaining of mouse tooth germs showed that S100a6 was expressed in ameloblasts but not in the undifferentiated dental epithelium. Additionally, S100a6 was localized to the calcification-forming side in enamel-forming ameloblasts. Moreover, siRNA-mediated S100a6 knockdown in ameloblasts reduced intracellular calcium concentration and the expression of ameloblast marker genes, indicating that S100a6 is associated with ameloblast differentiation. Furthermore, S100a6 knockdown inhibited the ERK/PI3K signaling pathway, suppressed ameloblast proliferation, and promoted the differentiation of the dental epithelium toward epidermal lineage. Conclusively, S100a6 knockdown in the dental epithelium suppresses cell proliferation via calcium and intracellular signaling and promotes differentiation of the dental epithelium toward the epidermal lineage.

Calcium and Neural Stem Cell Proliferation

Intracellular calcium plays a pivotal role in central nervous system (CNS) development by regulating various processes such as cell proliferation, migration, differentiation, and maturation. However, understanding the involvement of calcium (Ca2+) in these processes during CNS development is challenging due to the dynamic nature of this cation and the evolving cell populations during development. While Ca2+ transient patterns have been observed in specific cell processes and molecules responsible for Ca2+ homeostasis have been identified in excitable and non-excitable cells, further research into Ca2+ dynamics and the underlying mechanisms in neural stem cells (NSCs) is required. This review focuses on molecules involved in Ca2+ entrance expressed in NSCs in vivo and in vitro, which are crucial for Ca2+ dynamics and signaling. It also discusses how these molecules might play a key role in balancing cell proliferation for self-renewal or promoting differentiation. These processes are finely regulated in a time-dependent manner throughout brain development, influenced by extrinsic and intrinsic factors that directly or indirectly modulate Ca2+ dynamics. Furthermore, this review addresses the potential implications of understanding Ca2+ dynamics in NSCs for treating neurological disorders. Despite significant progress in this field, unraveling the elements contributing to Ca2+ intracellular dynamics in cell proliferation remains a challenging puzzle that requires further investigation.

New insights into the inter-organ crosstalk mediated by ChREBP

Carbohydrate response element binding protein (ChREBP) is a glucose responsive transcription factor recognized by its critical role in the transcriptional control of glycolysis and de novo lipogenesis. Substantial advances in the field have revealed novel ChREBP functions. Indeed, due to its actions in different tissues, ChREBP modulates the inter-organ communication through secretion of peptides and lipid factors, ensuring metabolic homeostasis. Dysregulation of these orchestrated interactions is associated with development of metabolic diseases such as type 2 diabetes (T2D) and non-alcoholic fatty liver disease (NAFLD). Here, we recapitulate the current knowledge about ChREBP-mediated inter-organ crosstalk through secreted factors and its physiological implications. As the liver is considered a crucial endocrine organ, we will focus in this review on the role of ChREBP-regulated hepatokines. Lastly, we will discuss the involvement of ChREBP in the progression of metabolic pathologies, as well as how the impairment of ChREBP-dependent signaling factors contributes to the onset of such diseases.

Blocking the interface region amongst S100A6 and RAGE V domain via S100B protein

The Ca²⁺-mediated S100 family protein S100A6 has a crucial task in various intracellular and extracellular activities thereby demonstrating a possible involvement in the advancement and development of malignant tumors. S100A6 has been found to associate with receptor for advanced glycation end products, RAGE, through its extracellular extension. This extension is famously identified as a prominent receptor for many S100 family associates. Additionally, S100A6 binds to S100B protein and forms a heterodimer. Thus, we consider the S100B protein to be a prospective drug molecule to obstruct the interacting regions amongst S100A6 and RAGE V domain. We applied the NMR spectroscopy method to locate the binding area amid the S100A6m (mutant S100A6, cysteine at 3rd position of S100A6 is replaced with serine, C3S) and S100B proteins. The ¹H-¹⁵N HSQC NMR titrations revealed the probable requisite dynamics of S100A6m and S100B interfaces. Utilizing data from the NMR titrations as input parameters, we ran the HADDOCK program and created a S100A6m-S100B heterodimer complex. The obtained complex was then superimposed with the reported complex of S100A6m-RAGE V domain. This superimposition displayed the possibility of S100B to be a potential antagonist that can block the interface area of the S100A6m and the RAGE V domain. Moreover, an in vitro cancer model using SW480 cells in water-soluble tetrazolium-1 assay (WST-1) showed a noticeable change in the cell proliferation as an effect of these proteins. Our study indicates the possibility to develop a S100B-like competitor that could play a key role in the treatment of S100- and RAGE-mediated human diseases.

Zooming into the Dark Side of Human Annexin-S100 Complexes: Dynamic Alliance of Flexible Partners

Annexins and S100 proteins form two large families of Ca²⁺-binding proteins. They are quite different both structurally and functionally, with S100 proteins being small (10–12 kDa) acidic regulatory proteins from the EF-hand superfamily of Ca²⁺-binding proteins, and with annexins being at least three-fold larger (329 ± 12 versus 98 ± 7 residues) and using non-EF-hand-based mechanism for calcium binding. Members of both families have multiple biological roles, being able to bind to a large cohort of partners and possessing a multitude of functions. Furthermore, annexins and S100 proteins can interact with each other in either a Ca²⁺-dependent or Ca²⁺-independent manner, forming functional annexin-S100 complexes. Such functional polymorphism and binding indiscrimination are rather unexpected, since structural information is available for many annexins and S100 proteins, which therefore are considered as ordered proteins that should follow the classical “one protein–one structure–one function” model. On the other hand, the ability to be engaged in a wide range of interactions with multiple, often unrelated, binding partners and possess multiple functions represent characteristic features of intrinsically disordered proteins (IDPs) and intrinsically disordered protein regions (IDPRs); i.e., functional proteins or protein regions lacking unique tertiary structures. The aim of this paper is to provide an overview of the functional roles of human annexins and S100 proteins, and to use the protein intrinsic disorder perspective to explain their exceptional multifunctionality and binding promiscuity.

S100A6 is a critical regulator of hematopoietic stem cells

The fate options of hematopoietic stem cells (HSCs) include self-renewal, differentiation, migration, and apoptosis. HSCs self-renewal divisions in stem cells are required for rapid regeneration during tissue damage and stress, but how precisely intracellular calcium signals are regulated to maintain fate options in normal hematopoiesis is unclear. S100A6 knockout (KO) HSCs have reduced total cell numbers in the HSC compartment, decreased myeloid output, and increased apoptotic HSC numbers in steady state. S100A6KO HSCs had impaired self-renewal and regenerative capacity, not responding to 5-Fluorouracil. Our transcriptomic and proteomic profiling suggested that S100A6 is a critical HSC regulator. Intriguingly, S100A6KO HSCs showed decreased levels of phosphorylated Akt (p-Akt) and Hsp90, with an impairment of mitochondrial respiratory capacity and a reduction of mitochondrial calcium levels. We showed that S100A6 regulates intracellular and mitochondria calcium buffering of HSC upon cytokine stimulation and have demonstrated that Akt activator SC79 reverts the levels of intracellular and mitochondrial calcium in HSC. Hematopoietic colony-forming activity and the Hsp90 activity of S100A6KO are restored through activation of the Akt pathway. We show that p-Akt is the prime downstream mechanism of S100A6 in the regulation of HSC self-renewal by specifically governing mitochondrial metabolic function and Hsp90 protein quality.

S100A6 protein: functional roles

S100A6 protein belongs to the A group of the S100 protein family of Ca2+-binding proteins. It is expressed in a limited number of cell types in adult normal tissues and in several tumor cell types. As an intracellular protein, S100A6 has been implicated in the regulation of several cellular functions, such as proliferation, apoptosis, the cytoskeleton dynamics, and the cellular response to different stress factors. S100A6 can be secreted/released by certain cell types which points to extracellular effects of the protein. RAGE (receptor for advanced glycation endproducts) and integrin β1 transduce some extracellular S100A6's effects. Dosage of serum S100A6 might aid in diagnosis in oncology.

Effect of S100A6 over-expression on β-catenin in endometriosis

AIM

S100A6 is over-expressed in several human tumors, including pancreatic carcinoma, malignant fibrous histiocytoma, breast, colon, and gastric carcinoma, but little is known about the role of S100A6 in endometriosis. The aim of the present study was to investigate the effect of S100A6 over-expression on β-catenin in endometrial stromal cells.

METHODS

Endometrial stromal cells were transfected with an hS100A6-expressing recombinant lentivirus construct. The expression of β-catenin was assessed using western blot and reverse transcription-polymerase chain reaction.

RESULTS

S100A6 over-expression promoted β-catenin expression at the RNA and protein levels, in endometrial stromal cells.

CONCLUSIONS

S100A6 induces expression of β-catenin in endometrial stromal cells.

The S100A6 calcium-binding protein regulates endothelial cell-cycle progression and senescence

Endothelial cells regulate many aspects of vascular physiology, including vasculogenesis and angiogenesis. The S100 family of calcium-binding proteins regulates many aspects of cell function but their roles in vascular physiology are less well understood. Herein, we investigated the expression and function of S100-related family members in endothelial cells. Analysis of total endothelial mRNAs using a human gene chip array revealed significant gene expression of the S100 calcium-binding protein family members S100A6, S100A10, S100A11 and S100A13. We then examined the expression and functional properties of the major S100 family member, S100A6, in vascular endothelial cells. Comparison of primary and transformed human cells revealed significant differences in S100A6 protein levels in these cells. In primary human endothelial cells, S100A6 was present in both the nucleus and the cytoplasm. To assess the function of endothelial S100A6, we depleted protein levels using RNA interference and this caused increased cell-cycle arrest in the G2/M phase under different conditions. S100A6 depletion caused a decrease in both cyclin-dependent kinase 1 (CDK1) and phospho-CDK1 levels, which are essential for eukaryote cell-cycle progression. S100A6 depletion also decreased expression of CDK1, cyclin A1 (CCNA1) and cyclin B (CCNB1) genes with effects on cell-cycle progression. Depletion of endothelial S100A6 levels also elevated β-galactosidase expression, which is an important hallmark of cellular senescence and exit from the mammalian cell cycle. We thus propose that S100A6 has an important role in regulating endothelial commitment to, and progression through, the cell cycle.

Immunohistochemical Characterization of S100A6 in the Murine Ovary

S100 proteins comprise a large family of Ca(2+)-binding proteins and exhibit a variety of intra- and extracellular functions. Despite our growing knowledge about the biology of S100 proteins in some tissues such as brain and smooth muscle, little is known about S100 proteins in the normal mammalian reproductive tissue. In the present study, we investigated the distribution pattern of S100A6 (alternatively named calcyclin) in the murine ovary by immunohistochemical study using specific antibody. S100A6 was localized substantially in the cytoplasm of luteal cells, with concomitant expression of S100A11, another S100 protein, but not in the other type of cells such as oocytes, follicle epithelial cells (granulosa cells), and cells of stroma including theca interna cells in the murine ovary. S100A6-immunoreactive corpora lutea (CLs) were divided into two types: homogeneously and heterogeneously stained CLs, and possibly they may represent differentiating and mature CL, respectively. Our regression analysis revealed that expression level of S100A6 positively correlated with that of cytochrome P450 11A, a steroidogenic enzyme in the heterogeously stained CL. These results suggested that S100A6 may contribute to differentiation of steroidogenic activity of luteal cells in a synergistic manner with S100A11 by facilitating some shared functions.

S100A6 (calcyclin) deficiency induces senescence-like changes in cell cycle, morphology and functional characteristics of mouse NIH 3T3 fibroblasts

S100A6 (calcyclin) is a calcium binding protein with two EF-hand structures expressed mostly in fibroblasts and epithelial cells. We have established a NIH 3T3 fibroblast cell line stably transfected with siRNA against S100A6 to examine the effect of S100A6 deficiency on non-transformed cell physiology. We found that NIH 3T3 fibroblasts with decreased level of S100A6 manifested altered cell morphology and proliferated at a much slower pace than the control cells. Cell cycle analysis showed that a large population of these cells lost the ability to respond to serum and persisted in the G0/G1 phase. Furthermore, fibroblasts with diminished S100A6 level exhibited morphological changes and biochemical features of cellular senescence as revealed by beta-galactosidase and gelatinase assays. Also, S100A6 deficiency induced changes in the actin cytoskeleton and had a profound impact on cell adhesion and migration. Thus, we have shown that the S100A6 protein is involved in multiple aspects of fibroblast physiology and that its presence ensures normal fibroblast proliferation and function.

Expression of S100A6 in cardiac myocytes limits apoptosis induced by tumor necrosis factor-alpha

S100A6 is induced in myocardium post-infarction in vivo and in response to growth factors and inflammatory cytokines in vitro. Forced expression of S100A6 in cardiomyocytes inhibits regulation of cardiac specific gene expression in response to trophic stimulation. To define regulation and function of S100A6, we characterized the human S100A6 promoter and mapped upstream regulatory elements in rat neonatal cardiac myocytes, fibroblasts, and vascular smooth muscle cells and defined a functional role for S100A6 in tumor necrosis factor-alpha-induced myocyte apoptosis. The functional S100A6 promoter was localized to region -167/+134 containing 167 upstream base pairs. The S100A6 promoter is regulated by positive (-361/-167 and -588/-361) and negative (-1371/-1194) elements. Tumor necrosis factor-alpha induced the maximal S100A6 promoter and transcription factor NF-kappaB (p65 subunit). Electrophoretic mobility shift showed that tumor necrosis factor-alpha induced p65 binding to a potential NF-kappaB-binding site at -460/-451. Chromatin immunoprecipitation analysis revealed p65 is recruited to the S100A6 promoter upon tumor necrosis factor-alpha stimulation. The NF-kappaB inhibitor caffeic acid phenethyl ester and mutation of the NF-kappaB-binding site inhibited S100A6 promoter activation by tumor necrosis factor-alpha. Tumor necrosis factor-alpha induced cardiac myocyte apoptosis. Specific inhibition of S100A6 using a small interfering RNA directed against S100A6 potentiated tumor necrosis factor-alpha-induced myocyte apoptosis, whereas overexpression of S100A6 by gene transfer prevented tumor necrosis factor-alpha-induced myocyte apoptosis by interfering with p53 phosphorylation. These results demonstrate that S100A6 is induced by tumor necrosis factor-alpha via an NF-kappaB-dependent mechanism, serving a role in homeostasis to limit tumor necrosis factor-alpha-induced apoptosis by regulating p53 phosphorylation.

Structure of the S100A6 complex with a fragment from the C-terminal domain of Siah-1 interacting protein: a novel mode for S100 protein target recognition

S100A6 is a member of the S100 subfamily of EF-hand Ca (2+) binding proteins that has been shown to interact with calcyclin binding protein/Siah-1 interacting protein (CacyBP/SIP or SIP), a subunit of an SCF-like E3 ubiquitin ligase complex (SCF-TBL1) formed under genotoxic stress. SIP serves as a scaffold in this complex, linking the E2-recruiting module Siah-1 to the substrate-recruiting module Skp1-TBL1. A cell-based functional assay suggests that S100A6 modulates the activity of SCF-TBL1. The results from the cell-based experiments could be enhanced if it were possible to selectively inhibit S100A6-SIP interactions without perturbing any other functions of the two proteins. To this end, the structure of the S100A6-SIP complex was determined in solution by NMR and the strength of the interaction was characterized by isothermal titration calorimetry. In an initial step, the minimal S100A6 binding region in SIP was mapped to a 31-residue fragment (Ser189-Arg219) in the C-terminal domain. The structure of the S100A6-SIP(189-219) complex revealed that SIP(189-219) forms two helices, the first of which (Met193-Tyr200) interacts with S100A6 in a canonical binding mode. The second helix (Met207-Val216) lies over the S100A6 dimer interface, a mode of binding to S100A6 that has not previously been observed for any target bound to an S100 protein. A series of structure-based SIP mutations showed reduced S100A6 binding affinity, setting the stage for direct functional analysis of S100A6-SIP interactions.

S100-annexin complexes--biology of conditional association

S100 proteins and annexins both constitute groups of Ca2+-binding proteins, each of which comprises more than 10 members. S100 proteins are small, dimeric, EF-hand-type Ca2+-binding proteins that exert both intracellular and extracellular functions. Within the cells, S100 proteins regulate various reactions, including phosphorylation, in response to changes in the intracellular Ca2+ concentration. Although S100 proteins are known to be associated with many diseases, exact pathological contributions have not been proven in detail. Annexins are non-EF-hand-type Ca2+-binding proteins that exhibit Ca2+-dependent binding to phospholipids and membranes in various tissues. Annexins bring different membranes into proximity and assist them to fuse, and therefore are believed to play a role in membrane trafficking and organization. Several S100 proteins and annexins are known to interact with each other in either a Ca2+-dependent or Ca2+-independent manner, and form complexes that exhibit biological activities. This review focuses on the interaction between S100 proteins and annexins, and the possible biological roles of these complexes. Recent studies have shown that S100-annexin complexes have a role in the differentiation of gonad cells and neurological disorders, such as depression. These complexes regulate the organization of membranes and vesicles, and thereby may participate in the appropriate disposition of membrane-associated proteins, including ion channels and/or receptors.

S100A6 (calcyclin) enhances the sensitivity to apoptosis via the upregulation of caspase-3 activity in Hep3B cells

S100A6 (calcyclin) is a small calcium-binding protein which has been implicated in several cellular processes such as cell cycle progression, cytoskeleton rearrangement, and exocytosis. Also the upregulation of S100A6 has been reported in a variety of tumors and linked to metastasis. However, exact intracellular roles of S100A6 related with apoptosis have not been clarified yet. Here we demonstrated that the upregulation of S100A6 enhances the cell death rate compared to the control under the apoptotic conditions. In exogenously S100A6 induced Hep3B cells, cell viability was significantly decreased compared with mock and S100A6-knockdown cells under calcium ionophore A23187 treatment. The exogenously introduced S100A6 significantly affected the caspase-3-like activity in programmed cell death through the enhanced caspase-3 expression, which was verified by promoter assay in wild or mutant S100A6-transfected Hep3B cells. Next, the promoter activity of caspase-3 was increased by 2.5-folds in wild-type S100A6-transfected cells compared to mutant 2 (E67K, mutant of EF-hand motif) or control. Our results suggest that S100A6 might be involved in the processing of apoptosis by modulating the transcriptional regulation of caspase-3.

Repression of the human adenine nucleotide translocase-2 gene in growth-arrested human diploid cells: the role of nuclear factor-1

Adenine nucleotide translocase-2 (ANT2) catalyzes the exchange of ATP for ADP across the mitochondrial membrane, thus playing an important role in maintaining the cytosolic phosphorylation potential required for cell growth. Expression of ANT2 is activated by growth stimulation of quiescent cells and is down-regulated when cells become growth-arrested. In this study, we address the mechanism of growth arrest repression. Using a combination of transfection, in vivo dimethyl sulfate mapping, and in vitro DNase I mapping experiments, we identified two protein-binding elements (Go-1 and Go-2) that are responsible for growth arrest of ANT2 expression in human diploid fibroblasts. Proteins that bound the Go elements were purified and identified by matrix-assisted laser desorption ionization time-of-flight mass spectrometry as members of the NF1 family of transcription factors. Chromatin immunoprecipitation analysis showed that NF1 was bound to both Go-1 and Go-2 in quiescent human diploid cells in vivo, but not in the same cells stimulated to growth by serum. NF1 binding correlated with the disappearance of ANT2 transcripts in quiescent cells. Furthermore, overexpression of NF1-A, -C, and -X in NIH3T3 cells repressed expression of an ANT2-driven reporter gene construct. Two additional putative repressor elements in the ANT2 promoter, an Sp1 element juxtaposed to the transcription start site and a silencer centered at nucleotide -332, did not appear to contribute to growth arrest repression. Thus, enhanced binding of NF1 is a key step in the growth arrest repression of ANT2 transcription. To our knowledge, this is the first report showing a role for NF1 in growth arrest.

Identification of a putative calcium-binding protein as a dioxin-responsive gene in zebrafish and rainbow trout

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD, dioxin) is a widespread environmental contaminant that causes multiple effects in vertebrates. TCDD elicits its toxicity through aryl hydrocarbon receptor (AhR)-mediated modulation of gene regulation, increasing intracellular free calcium, and inducing calcium-mediated apoptosis in cell culture. Two TCDD-responsive cDNAs, which encode putative calcium-binding proteins, have been isolated from zebrafish and rainbow trout. The zebrafish and rainbow trout sequences are 88% similar to each other at the amino acid level and are orthologs of the human S100A4 calcium-binding protein. In zebrafish liver cell culture, treatment with TCDD increases S100A4a mRNA abundance. In juvenile rainbow trout, S100A4 mRNA was constitutively expressed in the heart, kidney, intestine, and spleen, but not in the liver. Exposure to TCDD significantly increased rainbow trout S100A4 mRNA abundance in the rainbow trout kidney. Taken together, these findings demonstrate in zebrafish and rainbow trout that dioxin increases expression of this EF-hand calcium-binding protein gene in a tissue-dependent fashion. However, demonstration that the encoded S100A4 proteins actually bind calcium and play a role in dioxin toxicity will require further study.

Expression of calcium-binding S100 proteins A4 and A6 in regions of the epithelial sac associated with the onset of hair follicle regeneration

In order to elucidate the onset mechanisms of hair regrowth, we characterized the expression of metastasis and cell-growth-associated calcium-binding S100 proteins in the regenerating follicular epithelium. Hair-cycle-dependent expression of S100A4 and S100A6 was found in the epithelial sac regions (bulge area and hair germ) of mouse pelage follicles. Protein localization of S100A4 was confined to the bulge area, the region where the presumed follicular stem cells reside, during the catagen-telogen-anagen transitional periods, whereas S100A6 protein was distributed throughout the epithelial sac regions during anagen phase. Prior to entering anagen phase, however, both S100 mRNAs were upregulated in the epithelial sac. Despite the induction of extensive cell death in the bulge region after plucking, a new hair cycle was initiated following transcription of S100A6 in the hair germ. Upon wounding stimuli, both the outer root sheath and the basal layer of epidermis expressed S100A6 mRNA prior to hyper-proliferation. Once the epithelial sac was induced to transcribe both S100 genes, resting follicles were concomitantly rejuvenated. These results suggest that S100A4 and S100A6 might play important roles in the activation of stem cells at the onset of follicle regeneration.

Calcyclin (S100A6) binding protein (CacyBP) is highly expressed in brain neurons

The expression of a novel calcyclin (S100A6) binding protein (CacyBP) in different rat tissues was determined by Western and Northern blotting. Polyclonal antibodies against recombinant CacyBP purified from E. coli exhibited the highest reaction in the brain and weaker reaction in liver, spleen, and stomach. CacyBP immunoreactivity was also detected in lung and kidney. Densitometric analysis showed that the concentration of CacyBP in the soluble fractions of total brain and cerebellum is approximately 0.17 and 0. 34 ng/microg protein, respectively. Northern blotting with a specific cDNA probe confirmed the high level of CacyBP expression in the rat brain and lower levels in other tissues examined. Immunohistochemistry and in situ hybridization of rat brain sections revealed strong expression of CacyBP in neurons of the cerebellum, hippocampus, and cortex. The in situ hybridization detected CacyBP in hippocampus as early as P7 (postnatal day 7) and a peak of expression at P21, and the expression signal was preserved until adulthood. In the entorhinal cortex, the peak of expression was observed at P7, whereas in the cerebellum it was seen at P21. The results presented here show that CacyBP is predominantly a neuronal protein. (J Histochem Cytochem 48:1195-1202)

Induction of S100A4 gene expression inhibits in vitro invasiveness of human squamous cell carcinoma, KOSC-3 cells

S100A4 is considered functionally involved in metastasis and invasiveness of rodent and human mammary tumors. We screened the expression of S100A4 in human squamous cell carcinoma cell lines, and found 2 cell lines which were highly invasive, but did not express any noticeable extent of S100A4. To examine whether the expression of S100A4 regulated invasiveness of squamous cell carcinoma, we transfected S100A4 cDNA into KOCS-3 and HSC-4 squamous cell carcinoma cells. The transfectants from KOSC-3 cells expressing sense S100A4 decreased invasiveness by 80% compared with cells of the wild type or those with the vector only.

TBP-associated factors (TAFIIs): multiple, selective transcriptional mediators in common complexes

Transcription of eukaryotic structural genes requires the assembly of RNA polymerase II and the general transcription factors (GTFs) on the promoter to form a pre-initiation complex (PIC). Among these, TFIID is the major sequence-specific DNA-binding component; the other GTFs enter the PIC primarily through protein-protein interactions. TFIID is composed of the TATA-box-binding protein (TBP) and multiple TBP-associated factors (TAFIIs). Unexpectedly, TAFIIs have also been found in other multi-subunit complexes involved in transcription. Whereas TBP is a general transcription factor, a variety of in vivo studies have demonstrated that TAFIIs are highly promoter selective. Here I review studies on the role of TAFIIs in genome-wide transcription and their mechanism of action.

Demonstration of heterodimer formation between S100B and S100A6 in the yeast two-hybrid system and human melanoma

S100B (S100beta) and S100A6 (calcyclin) are two 10-kDa Ca2+- and Zn2+-binding proteins coexpressed in melanoma and cell-cycle regulated. These proteins are members of the S100 subfamily and are thought to exert their function through interaction with intracellular target proteins. In order to search for potential target proteins interacting with S100B, we used a yeast two-hybrid strategy with human S100B as bait to screen a human brain cDNA library. The fusion proteins interacting with the S100B bait were identified as S100B, S100A1, and S100A6. This indicates the potential of S100B to form homodimers and heterodimers with other members of the S100 subfamily. By Northern and Western blotting, S100B and S100A6 were shown to be expressed at high levels in a panel of human melanoma cell lines. S100B and S100A6 were coimmunoprecipitated from melanoma cell lysates in the presence of 100 microM Zn2+. Confocal microscopy demonstrated that both proteins were distributed throughout the cytoplasm and concentrated in the nucleus. The demonstration of an association and colocalization of S100B and S100A6 in melanoma supports the possibility that an S100B/S100A6 heterodimer plays a functional role in these cells.

The three-dimensional structure of Ca(2+)-bound calcyclin: implications for Ca(2+)-signal transduction by S100 proteins

BACKGROUND

Calcyclin is a member of the S100 subfamily of EF-hand Ca(2+)-binding proteins. This protein has implied roles in the regulation of cell growth and division, exhibits deregulated expression in association with cell transformation, and is found in high abundance in certain breast cancer cell lines. The novel homodimeric structural motif first identified for apo calcyclin raised the possibility that S100 proteins recognize their targets in a manner that is distinctly different from that of the prototypical EF-hand Ca2+ sensor, calmodulin. The NMR solution structure of Ca(2+)-bound calcyclin has been determined in order to identify Ca(2+)-induced structural changes and to obtain insights into the mechanism of Ca(2+)-triggered target protein recognition.

RESULTS

The three-dimensional structure of Ca(2+)-bound calcyclin was calculated with 1372 experimental constraints, and is represented by an ensemble of 20 structures that have a backbone root mean square deviation of 1.9 A for the eight helices. Ca(2+)-bound calcyclin has the same symmetric homodimeric fold as observed for the apo protein. The helical packing within the globular domains and the subunit interface also change little upon Ca2+ binding. A distinct homology was found between the Ca(2+)-bound states of the calcyclin subunit and the monomeric S100 protein calbindin D9k.

CONCLUSIONS

Only very modest Ca(2+)-induced changes are observed in the structure of calcyclin, in sharp contrast to the domain-opening that occurs in calmodulin and related Ca(2+)-sensor proteins. Thus, calcyclin, and by inference other members of the S100 family, must have a different mode for transducing Ca2+ signals and recognizing target proteins. This proposal raises significant questions concerning the purported roles of S100 proteins as Ca2+ sensors.

Molecular cloning of chicken calcyclin (S100A6) and identification of putative isoforms

A full-length cDNA encoding smooth muscle calcyclin (S100A6) was cloned from chicken gizzard, using reverse transcription - polymerase chain reaction techniques. The deduced amino acid sequence contains 92 residues with 12 substitutions and a 2 amino acid C-terminal extension when compared with human calcyclin. Calcyclin was purified from chicken gizzard by Ca2+-dependent hydrophobic chromatography, heat treatment, and anion-exchange chromatography. N-terminal sequencing of two CNBr peptides confirmed its identity as calcyclin. Two isoforms of calcyclin (A and B), which differ with respect to the presence or absence of a C-terminal lysine, were identified and the native protein was shown to exist as noncovalently associated homodimers (AA and BB) and heterodimers (AB). Incubation of purified calcyclin AA with an extract of chicken gizzard did not result in degradation of calcyclin A or appearance of calcyclin B, suggesting that calcyclin B is a bona fide isoform rather than a proteolytic fragment generated during purification. Western blotting of chicken tissues with anti-(gizzard calcyclin) indicated abundant expression of calcyclin in smooth muscle tissues, including esophagus, large intestine, and trachea, with lower levels in lung, heart, kidney, and brain, and none detectable in liver or skeletal muscle.Key words: Ca2+-binding proteins, calcyclin, smooth muscle, cDNA cloning, isoforms.

Serum- and polypeptide growth factor-inducible gene expression in mouse fibroblasts

Complex cellular processes such as proliferation, differentiation, and apoptosis are regulated in part by extracellular signaling molecules: for example, polypeptide growth factors, cytokines, and peptide hormones. Many polypeptide growth factors exert their mitogenic effects by binding to specific cell surface receptor protein tyrosine kinases. This interaction triggers numerous biochemical responses, including changes in phospholipid metabolism, the activation of a protein phosphorylation cascade, and the enhanced expression of specific immediate-early, delayed-early, or late response genes. In this review, I summarize the major findings obtained from studies investigating the effects of serum or individual polypeptide growth factors on gene expression in murine fibroblasts. Several experimental approaches, including differential hybridization screening of cDNA libraries and differential display, have been employed to identify mRNA species that are expressed at elevated levels in serum- or polypeptide growth factor-stimulated cells. These studies have demonstrated that serum- and growth factor-inducible genes encode a diverse family of proteins, including DNA-binding transcription factors, cytoskeletal and extracellular matrix proteins, metabolic enzymes, secreted chemokines, and serine-threonine kinases. Some of these gene products act as effectors of specific cell cycle functions (e.g., enzymes involved in nucleotide and DNA synthesis), others are required to successfully convert a metabolically inactive cell to a metabolically active cell that will eventually increase in size and then divide (e.g., glucose-metabolizing enzymes), and some actually function as positive or negative regulators of cell cycle progression. In conclusion, research conducted during the past 15 years on serum- and growth factor-regulated gene expression in murine fibroblasts has provided significant insight into mitogenic signal transduction and cell growth control.

Yeast TAF(II)145 required for transcription of G1/S cyclin genes and regulated by the cellular growth state

TFIID comprises the TATA box-binding protein and a set of highly conserved associated factors (TAF(II)s). yTAF(II)145, the core subunit of the yeast TAF(II) complex, is dispensable for transcription of most yeast genes but specifically required for progression through G1/S. Here we show that transcription of G1 and certain B-type cyclin genes is dependent upon yTAF(II)145. At high cell density or following nutrient deprivation, yeast cells cease division, enter a G0-like state, and terminate transcription of most genes. In this stationary phase, we find that the levels of yTAF(II)145, several other yTAF(II)s, and TBP are drastically reduced. Collectively, our results indicate that yTAF(II)145 and other TFIID components have a specialized role in transcriptional regulation of cell cycle progression and growth control.

Molecular cloning of up-regulated cytoskeletal genes from regenerating skeletal muscle: potential role of myocyte enhancer factor 2 proteins in the activation of muscle-regeneration-associated genes

A subtractive hybridization and cloning strategy was used to identify genes that are up-regulated in regenerating compared with normal skeletal muscle. The gastrocnemius muscle of CD1 mice was injected with a myotoxic agent (BaCl2). A cDNA library was constructed from the regenerating muscle, and was screened with subtracted probes enriched in genes up-regulated during regeneration. Cofilin and vimentin cDNA clones were isolated. Both cofilin and vimentin were demonstrated to be overexpressed in regenerating compared with non-regenerating muscle (17-fold and 19-fold induction respectively). Cofilin and vimentin mRNAs also exhibited an increased expression in C2C12 myoblasts and a decreased expression in differentiated myotubes. Analysis of the regeneration-induced vimentin enhancer/promoter region revealed a consensus binding site for the myocyte enhancer factor 2 (MEF2) transcription factors. Electrophoretic mobility-shift assays and in vivo reporter assays revealed that MEF2 DNA-binding activity and transcriptional activation are increased in regenerating skeletal muscle, indicating that they may play a role in the activation of muscle genes during regeneration. These data suggest that both cofilin (an actin-regulatory protein) and vimentin (an intermediate filament) may be key components of the cytoskeletal reorganization that mediates muscle cell development and adult skeletal-muscle repair.

Modulation of S-100 genes response to growth conditions in human epithelial tumor cells

Many new members of the S-100 genes are known to be associated with cell differentiation, malignant transformation, and cell cycle. Of the S-100 genes examined in the present study, calcyclin, calpactin I light chain and calvasculin were expressed in most human epithelial tumor cells, and their expression levels differed according to various growth conditions. Their transcribed levels differed depending on each cell line, but their expression patterns were similarly changed under growth-modulatory conditions. Their messenger RNA levels increased parallel to the S phase population of cells, and decreased at G1/G2 phases. In contrast, this expression diminished in tumor cells under growth-inhibitory conditions, such as treatment with topoisomerase II inhibitor VP-16 or phorbol 12-myristate 13-acetate.

The role of keratin proteins and their genes in the growth, structure and properties of hair

The importance of wool in the textile industry has inspired extensive research into its structure since the 1960s. Over the past several years, however, the hair follicle has increased in significance as a system for studying developmental events and the process of terminal differentiation. The present chapter seeks to integrate the expanding literature and present a broad picture of what we know of the structure and formation of hair at the cellular and molecular level. We describe in detail the hair keratin proteins and their genes, their structure, function and regulation in the hair follicle, and also the major proteins and genes of the inner and outer root sheaths. We discuss hair follicle development with an emphasis on the factors involved and describe some hair genetic diseases and transgenic and gene knockout models because, in some cases, they stimulate natural mutations that are advancing our understanding of cellular interactions in the formation of hair.

1H NMR assignments of apo calcyclin and comparative structural analysis with calbindin D9k and S100 beta

The homodimeric S100 protein calcyclin has been studied in the apo state by two-dimensional 1H NMR spectroscopy. Using a combination of scalar correlation and NOE experiments, sequence-specific 1H NMR assignments were obtained for all but one backbone and > 90% of the side-chain resonances. To our knowledge, the 2 x 90 residue (20 kDa) calcyclin dimer is the largest protein system for which such complete assignments have been made by purely homonuclear methods. Sequential and medium-range NOEs and slowly exchanging backbone amide protons identified directly the four helices and the short antiparallel beta-type interaction between the two binding loops that comprise each subunit of the dimer. Further analysis of NOEs enabled the unambiguous assignment of 556 intrasubunit distance constraints, 24 intrasubunit hydrogen bonding constraints, and 2 x 26 intersubunit distance constraints. The conformation of the monomer subunit was refined by distance geometry and restrained molecular dynamics calculations using the intrasubunit constraints only. Calculation of the dimer structure starting from this conformational ensemble has been reported elsewhere. The extent of structural homology among the apo calcyclin subunit, the monomer subunit of apo S100 beta, and monomeric apo calbindin D9k has been examined in detail by comparing 1H NMR chemical shifts and secondary structures. This analysis was extended to a comprehensive comparison of the three-dimensional structures of the calcyclin monomer subunit and calbindin D9k, which revealed greater similarity in the packing of their hydrophobic cores than was anticipated previously. Together, these results support the hypothesis that all members of the S100 family have similar core structures and similar modes of dimerization. Analysis of the amphiphilicity of Helix IV is used to explain why calbindin D9k is monomeric, but full-length S100 proteins form homodimers.

Molecular cloning of ictacalcin: a novel calcium-binding protein from the channel catfish, Ictalurus punctatus

Calcium is essential for a variety of functions in animals, including signal transduction, transmission of nerve impulses, and bone and scale growth. In freshwater adapted teleosts, blood calcium levels are maintained constant (2-4 mM) even at low external calcium concentration (< 0.01 mM). Epithelial cells in skin and gill have been implicated in calcium homeostasis. We have cloned a cDNA from Ictalurus punctatus, the channel catfish, that codes for ictacalcin, a novel member of the S100 family of calcium-binding protein. In-situ hybridization demonstrates ictacalcin mRNA is abundant in epithelial cells of olfactory rosette, barbel, skin and gill but not brain or muscle. The presence of ictacalcin protein in these tissues was confirmed by immuno-blot analysis. Tissue extracts and recombinant ictacalcin bind calcium with attendant changes in electrophoretic mobility indicative of changes in protein conformation. The calcium-binding activity and abundant localization of ictacalcin in epithelial cells of several tissues indicates that this protein plays an important role in catfish calcium homeostasis.

Effect of dexamethasone on insulin receptor mRNA levels, RNA stability and isotype RNA pattern in U-937 human promonocytic cells

The administration of 5 x 10(-6) mol/l dexamethasone transiently increased insulin receptor (IR) mRNA levels in U-937 human promonocytic cells, which reached the maximum level at 15 h of treatment. Dexamethasone treatment did not affect the IR mRNA half-life (approximately 4 h), suggesting that the increase is regulated at the transcriptional level. The stimulatory action of dexamethasone was not prevented by the simultaneous presence of the protein synthesis inhibitor cycloheximide, indicating that the induction of IR gene transcription occurs as a direct response to the action of the synthetic glucocorticoid. Finally, the A isoform (lacking exon 11) was found to be the only IR isoform present in both untreated and dexamethasone treated-U-937 cells.

Sp1 activates and inhibits transcription from separate elements in the proximal promoter of the human adenine nucleotide translocase 2 (ANT2) gene

Expression of the adenine nucleotide translocator 2 (ANT2) gene is growth regulated. We report a feature of the ANT2 promoter that involves a novel regulatory function for the Sp1 transfactor. We show that expression from the ANT2 proximal promoter is modulated through three Sp1 elements, two of which activate and one of which partially inhibits transcription. The inhibitor site, box C, is juxtaposed to transcription start (nucleotides -7 to -2). Sp1 bound to box C decreases transcription initiation. This was demonstrated by introducing mutations in box C which (a) increased chloramphenicol acetyltransferase expression in the transient transfection assay and (b) inhibited binding of both purified Sp1 and Sp1 in crude nuclear extracts. The activating elements (A and B boxes) are located at adjacent sites in the distal region of the proximal promoter. Mutation of either box inhibits transfection by 90%, indicating that they act in a synergistic manner. Supershift experiments with crude nuclear extracts showed that only Sp1 was bound to the three GC boxes. The finding that Sp1 acts as an activator/inhibitor within the same promoter region was verified in NIH3T3, HeLa, JEG3, and COS-1, indicating that this dual effect of Sp1 is widely preserved. These data suggest a unique role for Sp1 and raise the possibility that growth activation of the ANT2 gene is regulated by the interaction of Sp1 on the A, B, and C boxes.

Targeted deletion in astrocyte intermediate filament (Gfap) alters neuronal physiology

Glial fibrillary acidic protein (GFAP) is a member of the family of intermediate filament structural proteins and is found predominantly in astrocytes of the central nervous system (CNS). To assess the function of GFAP, we created GFAP-null mice using gene targeting in embryonic stem cells. The GFAP-null mice have normal development and fertility, and show no gross alterations in behavior or CNS morphology. Astrocytes are present in the CNS of the mutant mice, but contain a severely reduced number of intermediate filaments. Since astrocyte processes contact synapses and may modulate synaptic function, we examined whether the GFAP-null mice were altered in long-term potentiation in the CA1 region of the hippocampus. The GFAP-null mice displayed enhanced long-term potentiation of both population spike amplitude and excitatory post-synaptic potential slope compared to control mice. These data suggest that GFAP is important for astrocyte-neuronal interactions, and that astrocyte processes play a vital role in modulating synaptic efficacy in the CNS. These mice therefore represent a direct demonstration that a primary defect in astrocytes influences neuronal physiology.

A delayed-early response nuclear gene encoding MRPL12, the mitochondrial homologue to the bacterial translational regulator L7/L12 protein

We have characterized a new delayed-early response mRNA encoding a 21-kDa product (MRPL12) that accumulates during the G1 phase of growth-stimulated cells. MRPL12 is the mammalian homologue to chloroplastic and bacterial L12 ribosomal proteins. Immunofluorescence microscopy and cell fractionation indicate a predominant mitochondrial localization in various mammalian cell lines. The NH2-terminal 49 amino acids are necessary and sufficient to target the protein within the mitochondria and are probably cleaved off during import. MRPL12 proteins associated in vitro and cofractionate with ribosomal structures, as is the case for prokaryotic L12 proteins. Expression of a dominant inhibitory truncated protein leads to a severe reduction in cell growth by inhibiting mitochondrial ATP production. MRPL12 is the first mammalian mitochondrial ribosomal protein to be characterized.

The structure of calcyclin reveals a novel homodimeric fold for S100 Ca(2+)-binding proteins

The S100 calcium-binding proteins are implicated as effectors in calcium-mediated signal transduction pathways. The three-dimensional structure of the S100 protein calcyclin has been determined in solution in the apo state by NMR spectroscopy and a computational strategy that incorporates a systematic docking protocol. This structure reveals a symmetric homodimeric fold that is unique among calcium-binding proteins. Dimerization is mediated by hydrophobic contacts from several highly conserved residues, which suggests that the dimer fold identified for calcyclin will serve as a structural paradigm for the S100 subfamily of calcium-binding proteins.

Citrate utilization gene cluster of the Lactococcus lactis biovar diacetylactis: organization and regulation of expression

The transport of citrate in Lactococcus lactis biovar diacetylactis is mediated by the citrate permease P. This polypeptide is encoded by the citP gene carried by plasmid pCIT264. In this report, we characterize the citP transcript, identify a cluster of two genes cotranscribed with citP and describe their post-transcriptional regulation. The transcriptional promoter is located 1500 nucleotides upstream of the citP gene and the transcriptional terminator is positioned next to the 3'-end of this gene. The DNA sequence was determined of the region upstream of the citP gene, including the promoter. Two partially overlapping open reading frames, citQ and citR were identified, which could encode polypeptides of 3.9 and 13 kDa respectively. These two genes, together with citP, constitute the cit cluster. Moreover, an IS-like element located between the cit promoter and the citQ open reading frame was identified. This element includes an open reading frame ORF1, which could encode a 33 kDa polypeptide. A translational fusion between the citP and a cat reporter gene showed that translation of citR and citP is coupled, and regulated by CitR. The cit mRNA was subjected to specific cleavage after addition of rifampicin to the bacterial cultures. We propose that expression of the cit cluster is controlled at the post-transcriptional level by mRNA processing at a putative complex secondary structure and by translational repression mediated by CitR.

Drosophila 230-kD TFIID subunit, a functional homolog of the human cell cycle gene product, negatively regulates DNA binding of the TATA box-binding subunit of TFIID

A Drosophila cDNA encoding the largest TFIID subunit (p230) was isolated using a degenerate oligodeoxynucleotide probe based on an amino acid sequence of the purified protein. The entire cDNA sequence contains an open reading frame encoding a polypeptide of 2068 amino acids, corresponding to a calculated molecular mass of 232 kD. The deduced amino acid sequence showed a strong sequence similarity with the protein encoded by a human gene (CCG1) implicated in cell cycle progression through G1, suggesting that p230 may be a target for cell cycle regulatory factors. The recombinant protein expressed in Sf9 cells via a baculovirus vector interacts directly with the TATA box-binding subunit of TFIID (TFIID tau or TBP) from Drosophila, human, and yeast. Surprisingly, recombinant p230 inhibits the TATA box-binding activity and function of TFIID tau, suggesting that p230 interactions with TFIID tau, and possible modulations thereof by other factors may play an important role in TFIID function.

Epithelial-mesenchymal transitions during cell culture of primary thyroid tumors?

Fibroblast contamination of epithelial tumor cell cultures is of great concern when examining tumor cells in vitro for specific biochemical and cytogenetic changes. The observations of normal karyotypes in thyroid tumor cell cultures have raised the concern of whether residual tissue fibroblasts might obscure the cytogenetic analysis of transformed epithelial cells. We have characterized early passaged thyroid tumor cells to examine the proportions of epithelial and fibroblastic cell types. Cells were analyzed by immunocytology using antibodies recognizing the thyroid prohormone thyroglobulin, epithelial cytokeratins, and vimentin, a mesenchyme marker. Tumors consisted of one follicular adenoma and five papillary carcinomas. When examined by day 15 in culture, all cells contained filaments composed of vimentin, which most likely represents an adaptation to culture conditions. Double immunofluorescence staining for thyroglobulin and cytokeratin revealed the presence of not only epithelial but also spindle-like fibroblastoid cells possessing thyroid epithelial cell markers. The results suggest that in thyroid tumor cultures there is a unique cell type intermediate between epithelial and mesenchyme phenotypes that must be considered when performing cytogenetic analysis.

Cell cycle-dependent gene expression in V point-arrested BALB/c-3T3 cells

Density-arrested BALB/c-3T3 cells stimulated to proliferate in an amino acid-deficient medium arrest in mid-G1 at a point termed the V point. Cells released from V point arrest require 6 hr to traverse late G1 and enter S phase. As data presented here show that mRNA synthesis is needed for 2-3 hr after release of cells from the V point, after which inhibition of mRNA synthesis does not prevent entry into S phase, we used this mid-G1 arrest protocol to analyze gene expression in late G1. We found that although stimulation of cells in amino acid-deficient medium did not inhibit the induction of genes expressed in early G1, genes normally expressed in late G1 were expressed only after release from the V point. The expression of late G1 genes in cells released from the V point was temporally similar, in respect to G1 location, as was seen in stimulation of quiescent G0 cells. As this protocol effectively divides gene expression into early (pre-V point) and late (post-V point) categories, it should be useful in studies of growth factor-modulated events that regulate traverse of late G1 and commitment to DNA synthesis. In addition, we used c-myb antisense oligonucleotides to show that c-myb expression, which occurs in late G1, is required for BALB/c-3T3 fibroblasts to traverse late G1 and initiate DNA synthesis.

The gene encoding the calcium binding protein calcyclin is expressed at sites of exocytosis in the mouse

Calcyclin is a member of the S100 family of calcium binding proteins. We have found by in situ hybridization that calcyclin transcripts are restricted to specific cell types within a limited number of mouse organs. High levels of expression in the epithelia lining the gastrointestinal, respiratory and urinary tracts, and specific localization of the transcripts to the goblet cells in the small intestine, lead us to suggest a role for calcyclin in the process of mucus secretion. In addition, calcyclin expression was detected in the corpus luteum, placenta and nerves within the gut wall, which are all sites of regulated exocytosis. We propose that this S100-like protein may be part of a calcium signalling pathway utilized in the secretion of various products by different cell types.

Coordinated posttranscriptional control of gene expression by modular elements including Alu-like repetitive sequences

We previously reported that in rat fibroblasts, accumulation of a set of mRNAs ("pIL genes") was modulated as a function of cell growth and transformation, at a posttranscriptional stage, and by a mechanism that depends on a short nucleotide sequence containing an ID repetitive element. In mouse fibroblasts, hybridization with rat pIL probes identified mRNAs with the same pattern of expression, which did not contain ID sequences but contained a different regulatory element, encompassing a repetitive sequence of the B1 family. Expression in mouse cells of a reporter beta-globin gene carrying this element inserted in its 3' noncoding region was growth- and transformation-dependent. The nucleotide sequences of two murine and of three rat pIL cDNAs showed clear similarities in the region immediately adjacent to the ID and B1 repeats. Both the repeat and the flanking sequence were required to confer on beta-globin constructs the pattern of expression characteristic of the pIL genes. The hypothesis is presented that repetitive sequences in the eukaryotic genome might be modular parts of complex regulatory elements ensuring the coordinated expression of various mRNA species.